1. G.X.Z. Yuan, KKM Theory and Applications in Nonlinear Analysis, Marcel-Dekker, New York (1999).
2. D.K. Inderlehrer, G. Stampacchia, An Introduction to Variational Inequalities and their Applications, Academic Press, New York (1980).
3. S.S. Chang, Variational Inequality and Complementarity Problem Theory with Applications, Shanghai Scientific Technology and Literature Press, Shanghai (1991).
4. F. Facchinei, J.S. Pang, Finite-dimensional Variational Inequality and Complementarity Problems, Springer-Verlag, New York (2003).
5. Y.S. Lai, Y.G. Zhu, Y.B. Deng, The existence of nonzero solutions for a class of variational inequalities by index, Appl. Math. Lett., 16 (2003), 839–845.